ORIGINAL PAPER Thermal acclimation, mitochondrial capacities and organ metabolic profiles in a reptile (Alligator mississippiensis) Helga Guderley • Frank Seebacher Received: 28 February 2010 / Revised: 11 July 2010 / Accepted: 15 July 2010 / Published online: 1 August 2010 Ó Springer-Verlag 2010 Abstract Reptiles thermoregulate behaviourally, but change their preferred temperature and the optimal temperature for performance seasonally. We evaluated whether the diges- tive and locomotor systems of the alligator show parallel metabolic adjustments during thermal acclimation. To this end, we allowed juvenile alligators to grow under thermal conditions typical of winter and summer, providing them with seasonally appropriate basking opportunities. Although mean body temperatures of alligators in these groups differed by approximately 10°C, their growth and final anatomic status was equivalent. While hepatic mito- chondria isolated from cold-acclimated alligators had higher oxidative capacities at 30°C than those from warm- acclimated alligators, the capacities did not differ at 20°C. Cold acclimation decreased maximal oxidative capacities of muscle mitochondria. For mitochondria from both organs and acclimation groups, palmitate increased oligo- mycin-inhibited respiration. GDP addition reduced palmi- tate-uncoupled rates more in liver mitochondria from warm- than cold-acclimated alligators. In muscle mito- chondria, carboxyatractyloside significantly reduced pal- mitate-uncoupled rates. This effect was not changed by thermal acclimation. The aerobic capacity of liver, skeletal muscle and duodenum, as estimated by activities of cyto- chrome c oxidase (COX), increased with cold acclimation. At acclimation temperatures, the activities of COX and citrate synthase (CS) in these organs were equivalent. By measuring COX and CS in isolated mitochondria and tissue extracts, we estimated that cold acclimation did not change the mitochondrial content in liver, but increased that of muscle. The thermal compensation of growth rates and of the aerobic capacity of the locomotor and digestive systems suggests that alligators optimised metabolic processes for the seasonally altered, preferred body temperature. The precision of this compensatory response exceeds that typ- ically shown by aquatic ectotherms whose body tempera- tures are at the mercy of their habitat. Keywords Thermoregulation Á Ectotherm Á Growth rate Á Cytochrome c oxidase Á Citrate synthase Á Uncoupling Introduction For ectotherms, changes in habitat temperature can mark- edly influence body temperature and hence metabolic processes. When faced with prolonged decreases in habitat temperature, as during winter, fish that remain active show increases in tissue metabolic capacity that at least partially compensate for the impact of temperature (Guderley 2004; McClelland et al. 2006; LeMoine et al. 2008). Tissue aerobic capacity is a primary target of this thermal com- pensation with marked increases in mitochondrial volume density and in mitochondrial oxidative capacity occurring during cold acclimation. These changes can maintain equivalent capacities of aerobic ATP generation at a wide range of habitat temperatures (Guderley and St. Pierre 1999). Although such reactions are well established for temperate zone fish species, less is known concerning the compensatory responses of metabolic capacities for the Communicated by I. D. Hume. H. Guderley De ´p de Biologie, Universite ´ Laval, Que ´bec, QC G1K 7P4, Canada F. Seebacher (&) Integrative Physiology, School of Biological Sciences A08, University of Sydney, Sydney, NSW 2006, Australia e-mail: frank.seebacher@sydney.edu.au 123 J Comp Physiol B (2011) 181:53–64 DOI 10.1007/s00360-010-0499-1